Port fuel injectors and direct fuel injectors each have advantages and disadvantages for injecting fuel to an engine. For example, port fuel injectors may provide lower engine emissions at lower engine temperatures. On the other hand, direct fuel injectors may provide improved air-fuel ratio control, thereby improving vehicle emissions during warm engine operating conditions. By combining port fuel injectors with direct fuel injectors, it may be possible to leverage advantages of both types of fuel injectors.
A desired amount of fuel injected to an engine cylinder during an engine cycle (e.g., four strokes) may be allocated between port fuel injectors and direct fuel injectors. The allocation of fuel to each type of fuel injector may be referred to as a fuel fraction or a percentage of a total amount of fuel injected during the engine cycle via the respective port and direct fuel injectors. For example, 20% or 0.2 of a total amount of fuel supplied to an engine or cylinder during a cylinder cycle, or a 20% direct fuel injector fuel fraction, may be delivered via direct fuel injectors. The remaining 80%, or an 80% port fuel injector fuel fraction, may be delivered to the engine or cylinder via port fuel injectors. Thus, the direct fuel injectors supply a 20% fraction of fuel supplied during the cylinder cycle, and the port fuel injectors supply an 80% fraction of fuel supplied during cylinder cycle. The directly injected fuel fraction and the port injected fuel fraction may vary with engine operating conditions such as engine speed and engine load or intake manifold pressure. However, fuel puddles may form in cylinder intake ports when fuel is supplied by port injectors. Further, fuel puddles may form within a cylinder due to injecting fuel via direct injectors during some conditions. The mass of fuel puddles may increase or decrease during transient conditions leading to engine air-fuel ratio errors as the fuel puddles expand and contract due to engine operating conditions. Therefore, it may be desirable to provide a way of compensating for the formation and/or dispersal of fuel puddles for an engine that includes both port and direct fuel injectors.
The inventors herein have recognized the above-mentioned issue and have developed an engine fueling method, comprising: retrieving engine operating information from sensors; adjusting a direct fuel injection fuel fraction of a total amount of fuel injected to a cylinder based on the engine operating information; filtering the direct fuel injection fuel fraction; and adjusting an amount of fuel injected to the cylinder in response to a difference between the direct fuel injection fuel fraction and the filtered direct fuel injection fuel fraction.
By filtering a direct fuel injection fraction, it may be possible to provide the technical result of improved transient fuel control during conditions where an injected amount of fuel is varied in response to conditions that may increase or decrease mass of one or more fuel puddles in an engine. The transient fuel adjustment may decrease an amount of fuel injected when it is expected that fuel in a puddle is dispersed and combusted in an engine cylinder. The transient fuel adjustment may increase an amount of fuel injected when it is expected that fuel in the puddle is increasing instead of entering a cylinder and participating in combustion within the cylinder. The increase or decrease in amount of fuel injected may be adjusted based on a direct fuel injector fuel fraction so that changes in proportion of fuel injected by direct and/or port injectors is compensated. The compensation operates to provide an amount of fuel in a cylinder that is equivalent to a desired cylinder fuel amount, even when fuel puddle size is increasing or decreasing.
The present description may provide several advantages. In particular, the approach may improve vehicle air-fuel ratio control. Additionally, the approach may be integrated with existing transient fuel control strategies to reduce development costs. Further, the approach may provide both gain and time constant adjustments based on a direct injector fuel fraction so that even if a total mass of fuel injected to the engine does not increase, fuel amounts provided to direct and port injection fuel injectors may be adjusted to account for puddles of fuel related to port and direct fuel injection.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.